What's the earliest date in which the bicycle could have been invented? The chain and gears shold not need very advanced metallurgy, I think they would have been possible already during the Renaissance, or am I wrong? The tyres look much more difficult however: how feasible could a bycicle with wheels similar to those of a light chariot be?
Finally what could the possible uses be, apart from an extravaganza for bored nobles? Maybe as couriers in lands where horses or forage are at a premium? Or to have "flying companies" of infantry, similar to the mounted infantry of the late xixth century? Now that I think of it, the lack of good roads could be an insurmountable obstacles, as I would think that cross country bikes would be much more difficult to build earlier than OTL.
Has anyone ideas on this?